This invention relates generally to semiconductor protective devices utilized, for example, in suppressing transients in electronic circuits and more particularly to a metal oxide threshold switching device.
A metal oxide or MOX switching device consisting of a layer of polycrystalline refractory transition metal oxide, such as NbO.sub.2 grown on a conducting refractory substrate such as a single crystal NbO is known, having been developed at Yeshiva University by Paul M. Raccah, Teodoro Halpern and Soo Hee Shin, and being shown and described in U.S. patent application Ser. No. 529,222 now U.S. Pat. No. 3,962,715. This normally high resistance device has the characteristic of becoming a low resistance device when subjected to a high voltage pulse. It is also capable of handling currents in the order of 80 amperes while maintaining a response time shorter than 0.7 nanoseconds. Its use as a transient suppression device is furthermore disclosed in U.S. Pat. No. 3,973,224 entitled "Tandem Configuration for EMP Protection", G. K. Gaule, et al., Aug. 3, 1976.
This device is made by contacting the active region by either a point or wide area pressure contact or by bonding a gold ribbon to a sputtered metallized pad of niobium or aluminum. Such a technique, for example, is disclosed in U.S. Ser. No. 729,519, entitled "Metal Oxide Threshold Switch Contact", by Paul R. Laplante, et al., one of the inventors being the inventor of the subject invention. Such prior art devices, however, are subject to failure due to shorting caused by the penetration of the active layer by the contact supplied thereto. It is to this inherent shortcoming that the present invention is directed.